14.0 Introduction

As you have read earlier, oxygen \(\left(\mathrm{O}_2\right)\) is utilised by the organisms to indirectly break down simple molecules like glucose, amino acids, fatty acids, etc., to derive energy to perform various activities. Carbon dioxide \(\left(\mathrm{CO}_2\right)\) which is harmful is also released during the above catabolic reactions. It is, therefore, evident that \(\mathrm{O}_2\) has to be continuously provided to the cells and \(\mathrm{CO}_2\) produced by the cells have to be released out. This process of exchange of \(\mathrm{O}_2\) from the atmosphere with \(\mathrm{CO}_2\) produced by the cells is called breathing, commonly known as respiration. Place your hands on your chest; you can feel the chest moving up and down. You know that it is due to breathing. How do we breathe? The respiratory organs and the mechanism of breathing are described in the following sections of this chapter.